Predicting the distribution of mechanical stresses in the S. aureus cell wall during the cell cycle

Staphylococcus aureus is a Gram-positive bacterium which is clinically important due to its ability to act as an opportunistic pathogen and to generate antibiotic-resistant strains. During the cell cycle, the cell synthesizes a flat septum that divides the spherical cell into two hemispheres. Division then happens in few milliseconds, suggesting an important role for mechanics in the separation process. In this work, we used concepts from mechanical engineering to create an elastic model of the cell wall, in order to predict the spatial distribution of stress in the cell wall, and the induced deformations, during the cell cycle. Our modelling shows that the presence of the growing septum decreases the cell wall stress in its vicinity and leads to an invagination. The amount of this invagination and reduction in stress depends on the mechanical and geometrical properties of the cell wall and the septum. For a smaller cell with thicker wall, the stress is less during the whole cell cycle, and a stiffer septum leads to more invagination. Comparing these predictions with experimental data for various mutants in the presence and absence of cell-wall targeting antibiotics should provide a useful tool for understanding the role of mechanical stress in the S. aureus cell cycle.